Deferred Mail

I have recently installed Zimbra on a test server. The installation was successful and all services appear to be running. I can access the administration console and can access the web client. When I test sending mail from one Zimbra account to another it takes an inordinate amount of time to receive the email and appears to be getting deferred. I am unable to send any email outside the domain. There is an MX and A record for the server that is resolvable from the outside and inside. The status message on the deferred email says that it timed out and that the IP address of origin is 127.0.0.1. Shouldn't that IP address be the actual IP address of the server, rather than the local loopback? If so, what should I do?